The purpose of these experiments was to determine whether the inhalation of high concentrations (2000ppm) of methyl methacrylate vapor could be inferred to be associated with observable changes in gastric motor activity of chloralose-urethan anesthetized dogs. It was determined that short exposures to vapor in this concentration were associated with a decrease in ongoing gastric motor activity. The inhibitory effect was not blocked by bilateral vagotomy, splanchnectomy, spinal transection, or intravenous tetraethylammonium. It was also determined that a sample of arterial blood that was obtained during vapor inhalation would produce the same effect when administered intravenously to another dog that was not exposed to the vapor. Inasmuch as we have observed that the monomer vapor depresses the spontaneous motor activity of intestinal strips in vitro we believe that methyl methacrylate monomer vapor probably exerts a direct inhibitory effect upon gastrointestinal smooth muscle and that the cardiopulmonary system is capable of mediating this effect when exposure is by inhalation.